Surge protectors are in use to protect electronic components from the deleterious effects of electrical surges. Generally, surge protectors function to shunt abnormal surges of electricity away from electronic components. There are three major causes of electrical surges: lightning pulses, ground surges, and power crosses. Lightning pulses are a relatively brief surge of electricity stemming from a strike of lightning on or near an electrical conduit, such as a power line or a communications line. Ground surges are caused when excess voltage, which follows the path of least resistance, does not entirely travel to ground, but instead strays off to another line which is itself connected to ground. Ground surges may be caused by a shorted circuit, a faulty connection to ground, the intensity of the abnormal voltage level, or the duration of an abnormal voltage level.
A power cross is potentially the most devastating type of electrical surge. A power cross comes when a pole carrying power lines is toppled, such as by high wind, a tree falling against it, or a car running into it, and falls into another line, for example, a telecommunications cable or line. Upon the pole falling, the various lines may become dislodged and crossed. Crossed lines may remain so for a lengthy time, thus subjecting a line or cable and any electrical components in connection with it to abnormal voltage conditions for a lengthy period of time. Depending upon the intensity of the power cross, as well as its duration, the line or cable may be melted. If the line or cable is running in from an industrial site, such as, for example, a phone company, the amount of line or cable melted may be miles long. The replacement cost, as well as the cost of running new line or cable, is high.
Devices have been utilized on so called "twisted pair" telephone lines to protect against electrical surges since the 1920 s. One such device, described in U.S. Pat. No. 4,161,762 (Scheithauer), acts as a fuse. Specifically, the device operates if an excess current flows through the line. Devices such as the one described in Scheithauer are impractical for coaxial communications lines. In particular, placing a fuse in a coaxial communications line changes the characteristics of the coaxial cable by adding impedance to the center conductor. Changing the characteristics alters the signals being transmitted.
Surge protectors for cables have been described in U.S. Pat. No. 5,835,326 (Callaway), U.S. Pat. No. 5,751,534 (DeBalko), U.S. Pat. No. 5,726,851 (Knapp), and U.S. Pat. No. 5,508,873 (Knapp et al.).